1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus, and more particularly to a substrate processing method and a substrate processing apparatus for polishing a peripheral portion of a substrate to remove an unwanted film and planarize an uneven surface.
2. Description of the Related Art
In a large scale integrated circuit, various kinds of micromachining techniques have recently been studied and developed. In the design rule, micromachining on a submicron order has already been realized. As the need for a finer structure has become more severe, management of particles and impurity concentration has also become strict. In addition, it has been increasingly important to manage a peripheral portion as well as front and rear surfaces of a substrate. Under such circumstances, an etching technique using a chemical liquid and a polishing technique of removing an unwanted film from a substrate have been applied to a method of processing a peripheral portion of a substrate. Particularly, the polishing technique is excellent in removing a high chemical resistant material and in planarizing an uneven surface, and is therefore widely used in various kinds of processes.
This kind of polishing technique removes a film on a substrate by bringing a polishing surface of a polishing tool into sliding contact with the substrate at a certain pressure. As disclosed in Japanese laid-open patent publication No. 2003-234314, there are two types in this kind of polishing method: one is conducted while supplying polishing liquid, i.e., slurry, containing abrasive particles onto a contact portion between a substrate and a polishing surface of a polishing cloth such as a nonwoven fabric, and the other is conducted while supplying pure water onto a contact portion between a substrate and a polishing surface of a polishing tape having abrasive particles fixed thereto.
However, there are some problems in these polishing methods when polishing the peripheral portion of the substrate. Generally, a film on a peripheral portion of a substrate is not uniform in thickness, and the surface of the peripheral portion has irregularities with different heights. Further, the abrasive particles are not uniformly distributed over the peripheral portion, and the polishing cloth does not have a uniform structure. Thus, if polishing is performed in a fixed period of time, the surface of the peripheral portion cannot be uniformly finished. Specifically, the film, to be polished, may remain on the peripheral portion and the uneven surface may not be sufficiently planarized due to a lack of polishing, or a profile of the peripheral portion may change due to excessive polishing.
In a practical apparatus, a peripheral portion of a semiconductor substrate is polished as follows. A semiconductor substrate is attracted and held by a rotating stage and then the rotating stage is rotated. A polishing surface, which is attached to a polishing head, is brought into contact with the peripheral portion of the semiconductor substrate and presses the peripheral portion while pure water or a polishing liquid is being supplied onto the semiconductor surface, thereby polishing the peripheral portion. In this kind of apparatus, the semiconductor substrate is placed onto the center of the rotating stage by a transfer system such as a transfer robot. However, the semiconductor substrate may deviate from the center of the rotating stage due to several causes such as an error in repetitive operation of the transfer system, an abnormal operation of the transfer system, and an anomaly in a substrate holding mechanism during polishing.
The deviation from the center of the rotating stage causes instability in contact between the polishing tape and the substrate, and also causes instability in pressure applied to the substrate. As a result, a finished state of the peripheral portion is uneven, and, in the worst case, the substrate may crack during polishing. Therefore, it is necessary to grasp a degree of the anomaly in polishing so as to take appropriate measures.